1. Field of the Invention
This invention relates, in general, to photocopying and, more specifically, to sheet transporting systems in copiers, printers, duplicators, and like devices.
2. Description of the Prior Art
Electrostatographic apparatus, such as copiers, printers, and duplicators, can have many different basic forms of construction. One type of apparatus known in the prior art has a transfer drum which is dimensioned to be able to hold two copy sheets at the same time. U.S. Pat. No. 4,712,906, which issued on Dec. 15, 1987 to the same assignee as the present invention, discloses such apparatus. In the referenced patent, the transfer drum can handle one 11".times.17" copy sheet or two 81/2".times.11" copy sheets simultaneously. The ability to process two sheets at the same time increases the throughput speed of the machine when using the smaller sized sheets.
When color copying is employed, there is a gap between the times when copies are produced by the transfer station of the copier with either single or double sheet transfer. This gap is required because extra revolutions of the transfer drum are necessary to transfer all of the separate color images in registration to the copy sheets. Sometimes, as many as four revolutions are necessary to get all of the image frames transferred to a pair of 81/2".times.11" copy sheets. A subtle but nevertheless actual disadvantage of such a process is that the finished color copies are delivered to the machine fuser station at a non-constant rate when multiple copies of the original are being made with the multiple-sheet transfer system. This is an unusual occurrence to the operator and can cause some confusion as to when the copy operation is actually finished.
Many of the major subsystems in a copier or printer cannot change speed without affecting other characteristics of the machine's operation and performance. For example, if the speed of the fuser is changed, the amount of heat applied to the copy paper would be different than it is at the normal speed. To maintain consistency in the copies, a change in the temperature of the fuser would be needed with such a change in speed. Thus, changing the speed of the fuser is not usually desirable unless the amount of heat applied to the copy sheet can also be varied.
Therefore, in order to obtain a more expected and consistent output from a color copier or printer, it is desirable, and it is an object of this invention, to provide a control means for regulating the output rate at which copies are delivered by a machine which transfers to more than one color copy at a time.